Fluid transfer system and method

ABSTRACT

The present invention relates to a fluid transfer system and method for transferring fluid from a reservoir ( 2 ) and to (a) delivery device typically being (a) nozzle. The present invention relates in particular to transferring urea in highly accurate metered amounts from a reservoir ( 2 ) to a nozzle ( 5 ) arranged within an exhaust system ( 4 ) of a combustion engine ( 1 ) or combustion engines.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national phase application of and claims thebenefit of priority to PCT/DK/2006/050084, filed Dec. 22, 2006, whichdesignated the United States and was published in English and claims thebenefit of priority to Danish Patent Application No. PA 2005 01817,filed on Dec. 22, 2005. The disclosures of all of the aforementionedapplications are hereby expressly incorporated by reference in theirentirety.

The present invention relates to a fluid transfer system and method fortransferring fluid from a reservoir and to delivery device typicallybeing nozzle. The present invention relates in particular totransferring urea in highly accurate metered amounts from a reservoir toa nozzle arranged within an exhaust system of a combustion engine orcombustion engines.

INTRODUCTION TO THE INVENTION

It has been found that introduction of urea into the exhaust gassesstreaming from an combustion engine and into a catalytic system maydramatically increase the efficiency of the catalytic element'scapability to convert NOx gasses. While urea in it self is relativelyharmless to the environment and the amounts introduced into thecombustion system thereby can be overdosed, such wasting of urea isoften undesirably as the technology is often applied to moving vehiclesand such waste would require larger storage capacities than what isactually needed if urea is dosed correctly.

A need for introducing the required amount of urea into the exhaustgasses only is therefore present. Furthermore, urea is most efficientlyintroduced into the exhaust gasses as a spray of droplet which typicallyrequires that the urea is pressurised and fed to a nozzle.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a fluid transfersystem and method providing an efficient controllable delivery of fluidfrom a reservoir to a nozzle.

Thus, in a first aspect the present invention preferably relates to afluid transfer system for transferring fluid from a reservoir to areceiving device, preferably being a nozzle, the fluid transfer systemcomprising

-   -   a through flow device adapted to receive fluid from the        reservoir and transfer fluid through the system and/or measuring        the amount of fluid being transferred from the reservoir to the        receiving device,    -   a controllable shut-off valve arranged upstream of the receiving        device and preferably downstream of the through flow device,    -   a controlling unit controlling at least the state of the        shut-off valve        wherein the controlling unit is adapted to control the state of        the shut-off valve    -   so that the pressure of fluid being fed to the receiving device        is above a first pre-selected pressure limit (P_(min)), and/or    -   so that the delivered amount corresponds to a demand.

The through flow device may preferably comprise or is a dosing pump, apump, a measuring unit, a measuring pump, or a combination thereof.

In the present context a number of terms are used. Even though these areused in their ordinary meaning, a further exemplary explanation is givenon some of the terms.

Dynamical error in delivered amount: A dynamical error occurs when thedemand for delivered fluid varies with time and is caused by a delaybetween when the amount is delivered an when it should have beendelivered. The delay is typically due to elasticity in the fluiddelivery system, delay in prosecution of controlling and/or sensingsignal and/or the like. A dynamical error may be defined as the maximumvalue of the difference between the desired amount and the actualdelivered amount during a pre-defined time. The dynamical error is notaccumulated.

Accumulative error in delivered amount: An accumulative error indelivered amount is typically defined as an error which is not balancedover time.

Dosing pump: A unit delivering a precise amount of liquid controlled byan electrical signal from a control unit and which is capable of doingso against a high pressure.

Pump (p pump): A unit delivering an uncontrolled flow of liquid againsta high pressure or a unit capable of maintaining a high pressure.

Measuring unit: A unit giving information (most often as electricalsignals) about flow of liquid without influencing flow or pressure.

Measuring pump: A combination of a pump and the measuring unit.

Through flow device: A device adapted to receive fluid from a reservoirand transfer the fluid and/or measuring the amount of fluid beingtransferred from the reservoir and to a receiving device.

Demand: The amount to be delivered. Demand may be the immediate demandexpressed in e.g. liter per hour [l/h] or demand accumulated over aninterval expressed in e.g hour [h].

Delivery: The amount to be delivered. Delivery may be the immediatedelivery expressed in e.g. liter per hour [l/h] or delivery accumulatedover an interval expressed in e.g hour [h].

The invention involves preferably at least two ways of dosing fluid(further ways are explained later on). The first one may be summarisedin the following manner:

1. Use of a dosing pump: In such embodiments, the dosing pump providesvery accurately the amount demanded and the dosing pump is accordinglycontrolled to provide a delivery corresponding to a demand. Thepressurisation of the fluid is preferably obtained by a combination of afluid buffer arranged downstream of the dosing pump and a shut-off valvearranged downstream of the buffer.

The second one is based on using a measuring unit. In such embodiments,the fluid is pressurised in some manner; typically the fluid is storedpressurised in a reservoir or pressurised by a pump. A demand istypically expressed at regular intervals and the total amount to bedelivered in a given interval is typically estimated to equal the demand(in l/h) at the beginning of the interval multiplied with the length (inhour) of the interval. Use of a dosing unit may be summarised in thefollowing manner:

2a: The delivery of fluid can be estimated from a functionalrelationship giving delivered amount per hour multiplied by the openingtime of the shut-off valve. From such a relationship the time in a giveninterval the valve must be open for meeting a demand. During deliverythe actual delivered amount is measured by the measuring unit, and ifdiscrepancy is found between the estimated delivered amount and theactual delivered amount a feed back is made to the algorithm determiningthe opening time of the shut-off valve to take into account thediscrepancy.

2b: The actual delivery is measured during delivery. Once the demand ina given interval has been met, the shut-off valve is closed.

It should be noted that the above summaries are examples only, thatvariations of these two occurs and they are therefore not intended to beconstrued in a narrowing way. However, they are believed to provide anindication on a framework for the present invention. For instance, insome embodiments according to the present invention, the measuring unitand pressurisation unit are integrated into each other.

As it will appear in the following, a pump will in some embodimentpressurise fluid received from the tank. However, in some otherembodiment the system receives pressurised fluid from the tank and insuch embodiment the pump will not be necessary.

The present invention relates in a second aspect preferably to a methodof transferring fluid from a reservoir to a receiving device, preferablybeing a nozzle, the fluid transfer system comprising

-   -   a through flow device adapted to receive fluid from the        reservoir and transfer fluid through the system and/or measuring        the amount of fluid being transferred from the reservoir to the        receiving device,    -   a controllable shut-off valve (9) arranged upstream of the        receiving device and preferably downstream of the through flow        device,    -   a controlling unit controlling at least the state of the        shut-off valve        the method comprising controlling the state of the state of the        shut-off valve    -   so that the pressure of fluid being fed to the receiving device        is above a first pre-selected pressure limit (P_(min)), and/or    -   so that the delivered amount corresponds to a demand.

Also in this connection the through flow device may preferably compriseor is a dosing pump, a pump, a measuring unit, measuring pump or acombination thereof.

The controlling of the shut-off valve to meet a given demand ispreferably performed based on direct control of the shut-off valve basedon the system characteristic for obtaining a minimum dynamic error and acorrection signal from the measuring unit to modify an algorithm forcontrolling the valve in order to avoid accumulative error.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and in particular preferred embodiments thereofwill now be described in details with reference to the accompanyingfigures, wherein

FIG. 1 shows schematically a combustion system according to a preferredembodiment of the present invention,

FIG. 2 shows schematically a first embodiment of a fluid transfer systemunit according to the present invention,

FIG. 3 shows schematically three different flow regimes obtainable bythe fluid transfer systems according to the present invention,

FIG. 4 shows a second embodiment of the invention in a conceptual manner

FIG. 5 shows the a variant of the system in FIG. 4 where thepressurising and measuring function is combined,

FIG. 6 shows schematically an embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 4,

FIG. 7 shows schematically an embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 5,

FIG. 8 shows schematically another embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 5,

FIG. 9 shows schematically a third embodiment of a fluid transfer systemaccording to the present invention corresponding to FIG. 5,

FIG. 10 shows graphically an example on a strategy for delivery of ureaaccording to preferred embodiments of the present invention,

FIG. 11 shows graphically details on a strategy for delivery of ureaaccording to preferred embodiments of the present invention,

and

FIGS. 12 and 13 each show schematically preferred embodiments ofmeasuring units according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a combustion system comprising a combustion engine 1,typically being a Diesel engine, a tank 2 holding a liquid solution ofurea (also known under the trade name AdBlue) and a catalytic system 3.The exhaust of the engine 1 is connected to the catalytic system 3 by anexhaust pipe 4. The combustion system further comprising a nozzle 5connected to a fluid transfer unit 6 (broadly termed “a through flowdevice”) which is connected to the tank 2. The fluid transfer unit 6receives the liquid solution of urea and provides it to the nozzle 5 inamounts meeting the demand for urea in the catalytic system at least tosome extend.

FIG. 2 shows schematically the architecture of the fluid transfer unit(6 in FIG. 1) for introducing urea into the exhaust system of acombustion engine. Same numerals as used for designating elements inFIG. 1 are used for designating similar elements in FIG. 2. The systemarchitecture as shown in FIG. 2 comprises a dosing pump 7 connected atits inlet to the tank 2 for pumping and dosing urea to a buffer 8. Thebuffer 8 is via a shut-off valve 9 connected to the nozzle 5.

The dosing pump 7, of the embodiment according to FIG. 2, is a pumppressurising fluid and generating a controllable variable flow rate andthereby a controlled delivery. This means that the actual flow rate canbe controlled very precisely. The accuracy of the flow rate delivered bythe dosing pump 7 is typically lower than +/−1% of the full-scaledelivery when the delivery is larger than 10% of the full-scaledelivery. Below that amount, the accuracy is lower than +/−10% of thereading value being the amount the dosing pump 7 is set to provide. Thedosing pump is controlled by a motor control unit 11 which receivesinput representing the actual demand for urea and the motor control unit11 sets the dosing pump to pump this actual demand.

In order to render the different functions of the system of FIG. 2 morevisible, the motor control unit 11 and the shut-off valve control unit10 is shown as different elements of the system. However, those twounits may be assembled into a single unit. Basically, the two unitsserves the following two purposes:

-   -   Motor control unit 11, which on the basis of parameters defining        the state of the engine e.g. load and rpm defines the actual        demand for urea and signals the demand to the dosing pump 7. The        dosing pump 7 may be an ordinary dosing pump measuring an amount        of urea meeting the actual demand for urea and pressurise the        metered amount of urea to a pressure level being sufficient for        the nozzle to provide atomisation of the metered urea.    -   Shut-off valve control unit 10 controlling the state of the        shut-off valve i.e. changes the shut-off valve state from open        to close or vice versa on the basis of the pressure of the fluid        measured in the buffer 8 and at the same time provides a desired        distribution of the periods in which the shut-off valve is open.

All parts of the system may be integrated into a single unit. However,the tank and the nozzle are typically not integrated parts of thesystem, whereby the system may be placed at an appropriated place ofe.g. a truck.

The nozzle 5 is a nozzle that provides atomized fluid once the pressureof the fluid fed to the nozzle 5 is above a threshold P_(max). Abovethat threshold the amount of fluid being atomized equals the amount offluid provided by the dosing pump 7. However, below the threshold, thenozzle 5 will not be able to atomize all fluid, as the amount of fluidstreaming towards the nozzle is too small to build up a pressure abovethe threshold. When this occurs, the shut-off valve 9 controls whetherfluid is fed to the nozzle 5 or not in the manner disclosed below. Intypical applications the amount of fluid to be atomized ranges from e.g.0.1% to 100% of the maximum amount of fluid to be atomized andatomization of a continuous flowing fluid over such an interval istypically not considered feasible.

The shut-off valve 9 is a valve that opens when the pressure in thefluid pumped towards it is above a maximum pressure limit P_(max) (FIG.3) and closes once the pressure is below a minimum limit P_(min).P_(max) is typically 5% higher than P_(min) and P_(min) is the level atwhich it can be assured that the fluid fed to the nozzle 5 is atomizedby the nozzle 5. Below that pressure level, the nozzle 5 may be able toatomize but it can in general not be assured, as atomization requires apressure difference across the nozzle of a certain level. Thus, when theflow rate from the dosing pump 7 is to small to provide a pressure aboveP_(min), the shut-off valve closes and stays closed until the dosingpump 7 has pumped sufficient fluid to build up a pressure above P_(max).Once the pressure exceeds P_(max) the shut-off valve 9 opens and thefluid streams through the nozzle 5. During this streaming the amountbeing atomised is higher than what is delivered by the dosing pump 7 sothe pressure drops until P_(min) where the valve closes and a pressurebuild up is initiated again. By this procedure, the amount of fluidatomised in time average equal to the amount of fluid delivered by thedosing pump 7.

Referring to FIG. 3, this figure shows three different atomisationregimes, large flow (FIG. 3 a) medium flow (FIG. 3 b) and small flow(FIG. 3 c). As shown in FIG. 3 a the instantaneous pressure in the flowmeasured at the inlet of the shut-off valve 9 is after a whileconstantly above the limits of P_(max) and P_(min). If the demanddecreases, the amount of fluid pumped by the dosing pump 7 will decreaseresulting in a pressure decrease. The pressure can be decreased untilP_(min) and stay constant at a level above P_(min) as long as thedecrease occurs from a level being above P_(max). If the demand is verylarge or e.g. the nozzle 5 is clogged, the pressure may increase untilit reaches a safety limit P_(high) at which the dosing pump 7 stopspumping fluid but the shut-off valve 9 stays open.

When the demand for atomized fluid is at medium flow the atomisationenters into the regime disclosed schematically in FIG. 3 b. In thisregime, the pressure measured at the inlet of the shut-off valve 9 is atone instance lower than P_(max) and the shut-off valve 9 is accordinglyclosed; it is here assumed that the shut-off has not been opened, i.e.the state is reached from a level where the shut-off valve has beenclosed. As the shut-off valve 9 is closed and the dosing pump 7 is stillpumping, fluid will be accumulated in the buffer 8 and as the buffer 8is a resilient member accumulation of fluid therein will take placeresulting in that the pressure at the inlet of the shut-off valve 9 willincrease. This pressure increase will continue as long as the dosingpump 7 is pumping and the shut-off valve 9 stays closed. Once thepressure reaches P_(max) the shut-off valve 9 will open. Opening of theshut-off valve 9 will result in that fluid is streaming towards thenozzle 5. The fluid streaming towards the shut-off valve 9 is acombination of fluid being pumped by the dosing pump 7 and the change involume of the buffer 8. The effect of the decreasing buffer volume isindicated in FIG. 3 b with the dotted line denoted “pressure dropwithout inflow”. The amount of fluid pumped by the dosing pump 7 is, inthe regime shown in FIG. 3 b, insufficient to keep the pressure aboveP_(min), and once the pressure has dropped to P_(min) the shut-off valve9 closes where after accumulation of fluid in the buffer 8 begins,again, with an increasing pressure as a result. This cycle continues aslong as the demand for fluid is not changed. As it appears, the flowthrough the nozzle 5 in this regime will be pulsed and the time lengthof each pulse is the time from opening of the shut-off valve at P_(max)until closing of the shut-off valve at P_(min)

A minimum flow regime is schematically shown in FIG. 3 c. As shown inFIG. 3 c the pressure does not reach the limit of P_(max) being thepressure at which the shut-off valve 9 open for fluid flowing to thenozzle 5. In order to atomize fluid, the shut-off valve 9 is forced openat intervals, typically being at regular intervals. The time where theshut-off valve 9 is closed is in FIG. 3 c indicated by “set timeinterval” and the length thereof is pre-selected as the maximumallowable time for no delivery. The time length of a pulse is in FIG. 3c is indicated as “pulse time”. A cycle in this minimum flow regimecomprises two phases. The first phase begins (for instance) when thepressure is at P_(min) and the shut-off valve 9 closes. As the dosingpump 7 continues pumping the pressure increases as disclosed above inthe medium flow regime. When the set time interval has passed theshut-off valve 9 is forced open and as the fluid flows towards and outof the nozzle 5, the pressure decreases until the pressure reachesP_(min). By utilising this forced opening of the shut-off valve the timeintervals between two pulses can be kept lower than if one should awaita pressure build-up to P_(max) and as the intervals between two pulsescan be kept low one may be able to provide e.g. an even delivery of ureain the streaming exhaust gasses. The length of the time interval betweentwo pulses is typically pre-selected and is typically found byperforming experiments.

The various flow regimes, high, medium and minimum, are defined byselecting P_(max) and P_(min) in combination with selecting the lengthof “set time interval”. Actual values of these parameters are selectedin accordance with an actual nozzle configuration. In a typicalembodiment, P_(max) is selected to be 8.4 bar, P_(min) is selected to be8.1 bar and “set time interval” is selected to be one or a few seconds.In such embodiments, the minimum amount of fluid being fed to the nozzle5 is around 0.010 l/h, the flexibility of the buffer 8 is 160 mm³/bar.

The opening and closing of the shut-off valve 9 is electromagneticallycontrolled from a valve controlling unit 10 as shown in FIG. 2 by theconnection 12. The connection 12 transfers an electrical signal to theshut-off valve 9.

The buffer 8 may provide the effect that the frequency at which theshut-off valve 9 operates can be decreased compared to a system where nobuffer 8 is incorporated in the system.

When the shut-off valve 9 is closed and the dosing pump 7 pumps fluidthe pressure within the fluid transfer system increases. The fluid isconsidered to be incompressible and once the shut-off valve 9 is openedthe pressure in the fluid transfer system will, if no buffer 8 isincorporated and the dosing pump 7 is not pumping, drop to the leveloutside the nozzle 5 almost instantaneously. However, as the buffer 8 isa resilient member the contraction of the buffer's 8 volume willmaintain the pressure within the fluid transfer higher than P_(min) fora much longer period, thus the time between two consecutive openings ofshut-off valve 9 can be of sufficient length to secure a sufficient lifetime of the shut-off valve 9. Besides improving the valve life timeexpectancy the buffer will make it possible to use a much slower (andthus cheaper) valve. If the buffer is too big it can introduce anunacceptable dynamic error.

A pressure sensor 13 measures the pressure within the buffer 8. Themeasured pressure is used for controlling the state of the shut-offvalve 9 (open or close) and the pressure measured is used as if it wasthe pressure measured at the inlet of the valve. The measured pressureis signalled to a controlling unit 10 via the connection 14.

The connection 15 from the shut-off valve 9 to the nozzle 5 issufficiently stiff to assure that once the shut-off valve 9 is openedthe pressure increase in the connection 15 will in a substantial mannernot result in any deformation of the connection 15. If, on the otherhand, the connection was not substantially stiff, opening of theshut-off valve 9 would cause the connection 15 to expand resulting inthat the amount of urea streaming out of the outlet of the shut-offvalve 9 would not substantial instantaneously equal the amount streamingout of the nozzle 5 which normally would be considered as introducingerrors into the fluid transfer system. In order to provide suitablestiffness, the connection 15 is typically a line made of stainlesssteel. The stiffness of the connection 15 helps also to minimizedroplets from being formed at the outlet of the nozzle as theshutting-off of the shut-off valve if done sufficiently fast will resultin that no fluid will stream out of the nozzle. If, on the other hand,the connection 15 was not sufficiently stiff the connection wouldcontract once the shut-off valve is shut-off resulting in fluid beingforced out of the nozzle and a droplet formed at outlet of the nozzle.Such droplet may crystallise and result in clogging of the nozzle. It isnoted that such stiff connection may be applied to all the embodimentsof the invention.

FIG. 4 shows a second embodiment of the invention in a conceptualmanner. In contrast to the first embodiment where the dosing pump'sdelivery substantially equals the actual demand and the pressurisationis made by a combination of accumulating fluid in a buffer and a valve,the system of FIG. 4 is supplied with liquid at a constant pressure(within limits regardless of flow) from a pump 7 or alternatively from apressurised tank 18. Measuring unit 19 providing information on thedelivered amount measures the actual amount delivered. A motor/valvecontrol unit 20 operates the shut-off valve 9 typically and preferablypulsating in a PWM (pulse width modulated) manner in accordance with theactual need for urea in relation to system specific parameters such asnozzle constant, characteristics of the valve, pressure of the fluidbefore the nozzle etc. In this way a change in flow as demanded from themotor conditions will very quickly be provided through the nozzle 5 thusgiving a very little dynamic error. Signals via the connection 21 frommeasuring unit 19 will provide information for changing the PWM ofshut-off valve 9 in order to minimize the accumulative error.

FIG. 5 shows a variant of the system in FIG. 4 where the measuring unitand pump are combined into a single unit 22.

In the following FIGS. (6, 7, 8, and 9) different embodiments forpumping and measuring functions corresponding to FIG. 4 and FIG. 5 areshown. All the embodiments have among other potentials the potential toprovide a fast response (a small dynamic error) and a high accuracy (asmall accumulative error).

FIG. 6 shows an embodiment of the system corresponding to FIG. 4. Inthis embodiment the transfer system comprises a tank 18 containingpressurised fluid. Alternatively, the tank 2 may contain fluid atambient pressure and a pump 17 may provide pressurisation. At the outletof the tank 18 or the pump 17 a valve 23 is provided having its outletconnected to a measuring unit. The measuring unit comprises a piston 24attached to and acting on a membrane 25. As indicated in FIG. 6 themovement of the piston 24 and thus the membrane 25 is limited relativelyto the housing to which it is attached. The piston 24 is biased towardsthe membrane 25 by a spring 26. At the outlet of the measuring unit ashut-off valve 9 is provided which in dosing conditions acts asexplained above with respect to FIG. 4. In non-dosing conditions (whenpiston 24 is moved backwards and liquid is streaming into the measuringunit) the shut-off valve 9 must be closed. The valves 9 and 23 are bothmagnetic valves. Once the shut-off valve 9 is closed and the valve 23 isopened and the force from the fluid flowing through valve 23 and actingon the membrane is larger than the force on the piston 24 coming fromthe spring 26, the spring 26 will be compressed and the piston 24 willbe displaced until stopped by the facing of the house. This end positionis detected of the sensor 27 which through the connection 21 will signalto the control unit which in turn closes the valve 23 and startoperating shut-off valve 9. During this operation the biasing force fromthe spring 26 will displace the piston 24 in opposite direction therebypressing fluid being accumulated in the measuring unit towards theshut-off valve 9.

The fluid transfer system of FIG. 6 is used in the following manner.Initially, the shut-off valve 9 is closed and the valve 23 is opened.Once the valve 23 is opened the membrane 25 and the piston 24 movesagainst the biasing force from the spring 26. The valve 23 stays openuntil the displacement sensor 27 detects that the piston 24 has reachedits bottom position where no further compression of the spring 26occurs. The sensor sends a signal to the control unit 20 once the pistonhas reached its bottom position. Thereafter the valve 23 is closed andthe shut-off valve 9 is opened and operated in PWM mode until the pistonhas reached its top position. The sensor 27 signals this to the controlunit 20. As the displacement of the piston 24 corresponds to a deliveredamount of urea the delivered amount can be monitored by logging thesignal representing the upper or lower most position of the piston 24.Once the piston 24 reaches its upper most position, the shut-off valve 9is closed, the valve 23 is opened and the cycle is repeated.

Also this embodiment may be assembled into a unit as disclosed inconnection with the above embodiment.

FIG. 7 shows an embodiment of the system corresponding to FIG. 5. Inthis embodiment a combined pump/measuring unit performs thepressurisation of the fluid and gives information to the control unit 20about the amount delivered. Again, the transfer system comprising a tank2 connected to the pumping/measuring unit 22 via a valve 23. However, inthis embodiment, the valve 23 is a one-way valve and a further one-wayvalve 28 is arranged in the outlet of the pump/measuring unit. Thepumping in this embodiment also comprises a piston 24, a membrane 25 anda spring 26. The assembly of the piston 24, the membrane 25 and thespring 26 is slidable attached to a sub-piston 29. The sub-piston 29 isconnected via a connecting rod 30 to a crank 31 so that the rotation ofthe crank 31 results in a reciprocating displacement of the sub-piston29. The piston 24 will tend to follow this reciprocating displacement ofthe sub-piston 29. However, as the piston 24 is slidable arranged in thesub-piston 29 and biased by the spring 26 the displacement of the piston24 will differ from the displacement of the sub-piston 29.

Also in this embodiment, the transfer system is equipped with a sensor27 sensing the end positions in the relative movement between piston 24and sub-piston 29. A further sensor 32 is arranged for sensing the upperdead position of the crank 31.

When the sub-piston 29 is moved towards it lower position, the piston 24will once the spring 26 is fully expanded follow this displacement. Thiswill result in that the pressure above the membrane 25 is decreasedcausing the valve 23 to open and the valve 28 to close, thereby fluidwill be drawn from the tank and into the pump/measuring unit. When thesub-piston 29 thereafter moves towards it upper position the valve 23closes. During this displacement of the sub-piston 29, the spring willbe compressed as the shut-off valve 9 is closed during this movement andthe force from the pressure on the membrane 25 is larger than the forceapplied by the spring 26 on the piston 24. When the spring 26 has beenmaximally compressed and the crank 31 is stopped in upper dead position(signalled by the sensor 32 to the control unit 20) the nozzle canatomize urea in PWM mode as previously described and the spring 26 willstart to expand. Such expansion of the spring 26 will result in thatfluid may still be pressurised and delivered even though the crank 31 isnot rotating. In fact it may be essential for the function of the systemthat the shut-off valve 9 only is operated when the crank 31 and thusthe sub-piston is not moving.

FIG. 8 shows another embodiment of the system corresponding to FIG. 5.This embodiment has many similarities with the embodiment shown in FIG.7 and same numerals are used for similar elements. As in FIG. 6 themovement of the piston 24 and thus the membrane 25 is limited relativelyto the housing and not relatively to the sub-piston 29 whereby theprecision can be improved and the detection of end positions can besimplified. As shown in FIG. 8 the sub-piston 29 engages with the piston24 via a preloaded spring 33. In the top dead position there is aclearance between spring 33 and sub-piston 29 and in the lower deadposition the spring 33 can be slightly further compressed. This meansthat the movement of the crank mechanism is uncritical concerningprecision. Apart from this the function is as described in connection toFIG. 7.

FIG. 9 shows another embodiment of the system corresponding to FIG. 5.This embodiment comprises a pump/measuring unit connected at the inletto a tank via a one-way valve 23 and at the outlet of thepumping/measuring unit a one-way valve 28 is arranged. The two one-wayvalves 23 and 28 play the same role as the two one-way valves in anormal pump. The pump/measuring unit comprises a piston 24 and amembrane 25 similar to the piston and membrane of the above discussedembodiments. The piston 24 in this embodiment is directly connected to acrank 31 via a connecting rod 30.

The pump is typically controlled to maintain a substantially constantpressure at the shut-off valve 9. The shut-off valve 9 is typicallyopened and closed in a pulsating (PWM) manner based on the actual needfor urea. Due to the highly defined geometry each revolution of thecrank represents a well defined and known volume delivered, and a sensor32 may detect the amount pumped by picking up a signal for eachrevolution or a known fraction of a revolution. This detection isuncritical as an error is not accumulating. The signals will via theconnection 34 provide information for changing the PWM of shut-off valve9 in order to minimize the accumulative error.

The shut-off valve 9 can be operated without interruption in the earlierdescribed manner (PWM).

It should be noted the pump may have two membranes operating in oppositephases, one membrane having a suction stroke, while the other ispumping.

In the above a number of different embodiments are disclosed which eachdeals with delivery of liquefied Urea into an exhaust system. A commoncharacteristic of the different embodiments is the presence of ashut-off valve 9 arranged before the nozzle. Although the shut-off valvemay be dispensed with it is preferably applied in order to control theflow of urea to the nozzle; in some embodiments the shut-off valve is incombination with a buffer used to secure sufficient pressure of thefluid and in other embodiments used to control the amount of fluiddelivered to the nozzle. A combination thereof is, of course, alsopossible.

As indicated, delivery of urea according to the present invention maymainly be performed in four different manners:

I. Open loop operation: From the knowledge of system parameters (such asnozzle constant, pressure of the fluid before the nozzle, temperatureand viscosity of the fluid, characteristics of the shut-off valve etc.)the delivery of urea to the nozzle according to the need demanded(demand) from the motor control unit is controlled according to anadministering algorithm determining opening and closing periods for thevalve. The valve is operated solely on basis of system parameters (e.g.on basis of temperature and pressure measurements) without any feedbackfrom actually delivered volume. Typically, such an operation results ina high cost system.

II. Use of a dosing pump as shown FIGS. 2 and 3. The dosing pumpprovides a highly accurate flow rate and pressurisation is provided by acombination of a buffer and an administering valve; in FIG. 2 theadministering valve is termed shut-off valve.

III. Use of a measuring pump maintaining an approximately constantpressure being high enough to ensure atomization. The measuring pumppressurises the fluid and signals to a motor control unit that a welldefined amount of urea has been delivered. This is indicated in FIG. 5in which the measuring pump is referenced with numeral 22.

IV. Use of a measuring unit as shown in FIG. 4. Use of a measuring unitis especially advantageous in situations where urea is to be added atseveral locations and/or where easy access to pressurisation (e.g.pressurised air) is present. Various embodiments of measuring units aredepicted in FIGS. 12 and 13. Operation of the administering valve may bedone in a similar manner as when a measuring pump is used (FIG. 10).

FIG. 10 shows graphically an example of a strategy for delivery of ureaaccording to preferred embodiments of the present invention. Thestrategy is based on PWM (pulse width modulation). Although PWM and PIM(pulse interval modulation) may both be applied in connection with thepresent invention, it has been found that due to the large dynamic spanof delivery (more than a factor 100 between the largest and smallestdelivery amount per time unit) PIM seems to be less useable due to afixed pulse width, as the width of the pulses must be small in order todeliver small amounts without very large pulse intervals resulting inthat the shut-off valve at larger delivery has to be activates manytimes which in turn results in lower lifetime for the valve.

PWM provides the possibility to choose a suitable pulse interval whiletaking into account the dynamics (typically the buffer effect) of thecatalytic system.

The strategy shown in FIG. 10 is based on comparing accumulated deliverywith accumulated demand at certain points in time (when the measuringpump or the measuring unit send information about delivered amounts tothe motor/valve control unit). Based on this information the algorithmfor controlling the width of the pulses is changed in order to maintaina good accuracy.

In FIG. 10 C0, C1, C2, C3, C4 and C5 represent points in time whereaccumulated delivery is compared with accumulated demand. The immediatedemand (ml/s, labelled demand in FIG. 10) is prescribed by a controllingunit, typically a motor controlling unit. The accumulated demand (ml),delivered amount (ml/s, labelled delivery (pulses)) and accumulateddelivery (ml) are indicated in FIG. 10. Accumulated values maypreferably be determined by integration. For illustration theaccumulated curves are showed as continuous curves but in praxis thecontrol unit will compare values at interval (C1, C2, . . . etc.) andcalculate a single deviation value for use in the next interval (as willbe seen in FIG. 11).

The administrating algorithm determining activation of the shut-offvalve (pulse width) may comprise a number of elements, such asdeviations in the accumulated delivery from accumulated demand, error inaccumulated delivered amount between two feed back times, the rate ofchange at which such error changes etc.

With reference to FIG. 10 delivery is made with a constant pulse withineach interval if the demand is constant. At C1, the accumulated deliveryis compared to the accumulated demand and it is found that the deliveryhas been too high. Consequently, the pulse width is decreased at C1 andkept constant from C1 to C2. At C2 the accumulated demand is againcompared to the accumulated delivery and it is found that theaccumulated delivery still is higher than the accumulated demandalthough the accumulated delivery is approaching the accumulated demand.Consequently, the pulse width is decreased further.

Between C2 and C3 the demand for delivery is increased and as theaccumulated demand is higher than the accumulated delivery at C3, thepulse width is consequently increased in order to increase the delivery.At C4 it is found that the increase is not sufficient to meet the demandand at C4 the pulse width is again increased.

A more realistic situation with varying demand and thus varying pulsewidth within an interval is shown in FIG. 11. Here is shown a singleinterval Cn−Cn+1 with the same line labelling as in FIG. 10. Pulse widthis determined of the motor/valve control unit as a function of systemparameters (nozzle constant, pressure of the fluid at the shut-up valve,viscosity of the fluid, valve characteristic etc.) the need of deliveryflow at the start of a pulse and the time distance between pulses. Thevalue will be approximately Fdemand/Fmax*Tp, where Fdemand denotes theneed of delivery flow at the start of a pulse, Fmax stands for the flowwith an open shut-up valve and Tp is the time between two subsequentpulses. When the volume V(control) has been delivered from the measuringpump (at time Cn+1) the correcting signal is sent to the motor/valvecontrol unit and the accumulated demand is compared to V(control). Thesurplus (V(control)−V(Cn−1−Cn)) and the known accumulated error at Cn(ΔCn) determines the accumulated error at time Cn+1.

Obviously there exist a number of strategies to modify the algorithm forpulse width in the following interval. A simple one is aiming to deliverthe accumulated demand volume for the next interval (that meansΔCn+1=ΔCn+2) by multiplying the pulse width function by a factor(ΔCn−ΔCn+1)/V(control). Of course it will never be absolutely correct asthe demand is varying but as this variation is continuous and intervalsare rather short it will give a serviceable approximation. Anotherstrategy will be to aim to have zero accumulative error (ΔCn+2=0).

Embodiments which advantageously can be used in connection with theabove strategy are shown in FIGS. 12 and 13. FIG. 12 shows a measuringunit 19 shaped as a corbie-stepped piston device. However, theembodiments of FIGS. 12 and 13 are applicable in connection with otherstrategies.

The measuring unit 19 comprising a cylinder 39 in which a corbie-steppedpiston 38 is slideable arranged. The corbie-stepped shape of the piston38 is provided by the piston part 38 c whereby the area 38 a is largerthan the area 38 b as shown in the figure. The measuring device 19receives fluid through valve 36. The fluid is pressurised to a pressureP and is received from pressurised reservoir or a pump. The outlet ofvalve 36 connected to the larger displacement volume 40 a of cylinder39, and connected to the smaller displacement volume 40 b of thecylinder 39 via a valve 37. The connection between the valve 37 and thesmaller displacement volume 40 b also comprises a discharge 41 in theconfiguration shown in FIG. 12.

Above the end of the piston part 38 c opposite the end connected to thepiston 38 a displacement volume 42 is provided. This displacement volume42 receives fluid at the same or substantial same pressure P as fed tothe valve 36. In a preferred embodiment, the fluid supplied to valve 36and displacement volume 42 comes from the same source.

FIG. 12 shows two modes of the measuring device. In the upper part ofFIG. 12, valve 36 is open and valve 37 is closed whereby fluid atpressure P streams towards the larger displacement volume 40 a. As thearea of the top of the piston part 38 c is smaller than the area 38 aand the pressure in displacement volumes 40 a and 42 are equal, thepiston 38 will be displaced to the right with reference to FIG. 12. Theright-going movement results in that fluid present in displacementvolume 40 b is pressed out through the discharge 41. This actioncontinues until the piston 38 reaches its right-most position at whichposition valve 36 is closed and 37 is opened; this situation isdisclosed in lower part of FIG. 12.

When valve 36 is closed and valve 37 is open, the pressure indisplacement volume 42 will push the piston 38 to the left withreference to FIG. 12. Fluid present in displacement volume 40 a willflow out, through the valve 37 and into the displacement volume 40 b aswell as out through the discharge 41. This left-going action continuesuntil the piston 38 reaches its left-most position, when the states ofthe valves 36 and 37 are both changed and the cycle repeats.

The embodiment of FIG. 12 has among other advantages that the deliveryis present except at the left-most and right-most positions of thepiston and that the pressure of the fluid delivered to the discharge 41is well defined. Furthermore, a strong geometrical relationship ispresent between the amount of fluid delivered through discharge 41 andthe movement of the piston part 38 c.

The size of the areas 38 a and 38 b may be selected so that the sameamount delivered to the discharge irrespective of the way the piston 38moves. This may be achieved when the size of area 38 a is twice the sizeof area 38 b. Furthermore, the sizes of the displacement volumes havethe following ratio 2:1:1 (40 a:40 b:42). Embodiments like the one shownin FIG. 12 has the further advantages that the direction change of thepiston 38 can be performed very quickly and thereby only littleinterruption in fluid delivery is present (the directional change istypically governed by the speed at which the state of the valves can bechanged). In other embodiments where a suction stroke is present theinterruption is comparable larger.

By arranging the valves 36 and 37 as indicated on FIG. 12 redirectionvalves are not needed and the relatively simpler shut-off valves may beapplied.

FIG. 13 shows an embodiment similar to the embodiment of FIG. 12.Features of the embodiment shown in FIG. 13 which are similar tofeatures shown in FIG. 12 have been labelled with the same numerals.Similarly, the upper part of FIG. 12 shows a situation where the piston38 moves to the right, and the lower part shows a situation where thepiston moves to the left.

In the embodiment of FIG. 13, sealing membranes 43 a and 43 b areprovided between the piston 38 and the displacement volume 40 a andbetween the piston part 38 c and the displacement volume 42. Thepresence of the sealing membranes 43 a and 43 b provides a sealhindering fluid from flowing between the volumes 40 a and 40 b pass theedge of the piston 38.

Even though, the present description has focused on differentembodiments each having distinct features it should be emphasised thatfeatures disclosed in connection with one embodiment is applicable inconnection with another embodiment.

1. A fluid transfer system for transferring fluid from a reservoir (2)to a receiving device, the fluid transfer system comprising: a throughflow device (6) adapted to receive fluid from the reservoir (2) andtransfer fluid through the system and comprising a measuring unitadapted to measure the amount of fluid being transferred from thereservoir to the receiving device, a controllable shut-off valve (9)arranged upstream of the receiving device and downstream of the throughflow device (6), a controlling unit controlling at least the state ofthe shut-off valve (9) wherein the controlling unit is adapted tocontrol the state of the shut-off valve so that the delivered amountcorresponds to a demand in such a way that the controlling comprisesoperating the shut-off valve in PWM-mode (pulse width modulation-mode),and wherein the controlling unit is adapted to determine the accumulateddemand for a given interval, accumulate the delivery during at leastpart time of the interval by the measuring unit and adapt the width(s)of one or more pulses in said interval so that the accumulated deliveryin said intervals equals the accumulated demand.
 2. A fluid transfersystem according to claim 1, wherein the through flow device furthercomprises a pump.
 3. A system according to claim 1, wherein the shut-offvalve (9) is an electromagnetic valve.
 4. A system according to claim 1,further comprising a pressure sensor (13) arranged to measure thepressure of the fluid at a location upstream of the shut-off valve (9).5. A system according to claim 1, further comprising a valve (23)arranged upstream of the through flow device.
 6. A system according toclaim 5, wherein the through flow device comprises a piston (24) and amembrane (25), the piston is abutting, such as engaging, the membrane(25).
 7. A system according to claim 6, further comprising adisplacement sensor (27, 32) sensing the displacement of the piston(24).
 8. A system according to claim 6, further comprising a spring (26)being arranged so that the spring (26) is biasing the piston (24)towards the membrane (25).
 9. A system according to claim 6, wherein thepiston (24) is in slideable engagement with a sub-piston (29), and thesub-piston (29) is connected to a crank (31) by a connecting rod (30).10. A system according to claim 9, further comprising a one-way valve(28) arranged upstream of the shut-off valve (9) so as to allow fluid toflow towards the shut-off valve (9) only, and wherein the valve (23)arranged upstream of the through flow device is a one-way valve allowingfluid to flow towards the through flow device only.
 11. A systemaccording to claim 6, wherein the piston (24) is connected to a crank(31) by a connecting rod (30).
 12. A system according to claim 11,further comprising a one-way valve (28) arranged between the throughflow device and the shut-off valve (9), the one-way valve (28) isarranged to allow fluid to flow towards the shut-off valve (9) only. 13.A system according to claim 5, wherein the through flow devicecomprises: a measuring unit (19), the system comprising: a cylinder (39)in which a corbie-stepped piston (38) is slideable arranged, so as toprovide two displacement volumes (40 a, 40 b) of different sizes and asecond valve (37), wherein the inlet of the valve (36) arranged upstreamof the through flow device is connected to or connectable to a fluidsource, and the outlet of said valve (36) is connected to the larger ofthe displacement volumes and to the inlet of the second valve (37), theoutlet of the second valve (37) being connected to the smaller of thedisplacement volumes and to a discharge.
 14. A system according to claim13, wherein the cylinder (39) further comprises a further displacementvolume (42) provided above a piston part (38 c) forming part of thepiston (38), the displacement volume (42) being connected to orconnectable to a fluid source, preferably being the same fluid source towhich the inlet of valve (36) is connected to or connectable to.
 15. Asystem according to claim 14, wherein the two displacement volumes (40a, 40 b) are sealed from each other by a membrane (43 a) wherein thesmaller displacement volume (40 b) is sealed from the furtherdisplacement volume (42) by a membrane (43 b).
 16. A system according toclaim 1, further comprising a fluid connection (15) extending from theshut-off valve (9) to the receiving device, the connection is stiff soas to avoid expansion of the connection (15) which would causeuncontrollable flow through the connection due to contraction of theconnection (15) when the shut-off valve (9) is closed.
 17. A systemaccording to claim 1, further comprising the reservoir (2).
 18. A systemaccording to claim 1, wherein the receiving device is a nozzle (5). 19.A system according to claim 18, wherein the nozzle (5) is arranged in anexhaust system so that it sprays fluid into the exhaust system.
 20. Anexhaust system comprising a fluid transfer system according to claim 1.21. A method of transferring fluid from a reservoir (2) to a receivingdevice, the fluid transfer system comprising: a through flow device (6)adapted to receive fluid from the reservoir (2) and transfer the fluidthrough the system and comprising a measuring unit adapted to measurethe amount of fluid being transferred from the reservoir to thereceiving device, a controllable shut-off valve (9) arranged upstream ofthe receiving device and downstream of the through flow device (6), acontrolling unit controlling at least the state of the shut-off valve(9) the method comprising controlling the state of the state of theshut-off valve so that the delivered amount corresponds to a demand,wherein the controlling comprises operating the shut-off valve inPWM-mode (pulse width modulation-mode), and wherein the controlling unitis adapted to determine the accumulated demand for a given interval,accumulate the delivery during at least part time of the interval by themeasuring unit and adapt the width(s) of one or more pulses in saidinterval so that the accumulated delivery in said intervals equals theaccumulated demand.
 22. A method according to claim 21, wherein thethrough flow device further comprises a pump.
 23. A method according toclaim 21, further comprising measuring the pressure of the fluid at alocation upstream of the shut-off valve (9) and downstream of the pump(7).
 24. A method according to claim 21, wherein the controlling of theshut-off valve comprises closing the shut-off valve once the accumulateddelivery has reached the accumulated demand in said interval.
 25. Amethod according to claim 21, the method comprising: A) operating theshut-off valve in PWM-mode with one or more pulse widths in a timeinterval, B) at the end of said time interval comparing the accumulateddelivery with the accumulated demand, C) at the end of said timeinterval setting the pulse width(s) of the PWM-mode for a succeedingtime interval in response to the comparison and operating the shut-offvalve with the so changed pulse width(s) in an succeeding interval, D)repeating steps B) and C).
 26. A method according to claim 25, furthercomprising setting the pulse width(s) while delivering during saidinterval.
 27. A method according to claim 21, wherein setting of thepulse width(s) comprises adjusting an administering algorithm.
 28. Amethod according to claim 25, wherein the pulse width(s) are varyingduring a time interval.
 29. A method according to claim 25, wherein thepulse width(s) are equal during a time interval.
 30. A method accordingto claim 25, wherein the accumulated delivery is the amount deliveredsince a selected point in time, and the accumulated demand is the amountdemanded since the selected point in time.
 31. A method according toclaim 30, wherein the selected point in time is an instant where theaccumulated demand and accumulated delivery is reset, such as when thedelivery is initiated.
 32. A method according to claim 30, wherein aselected point in time is at the end of a last selected time period sothat method is performed in a cyclic manner.
 33. A method according toclaim 21, wherein the fluid is urea or urea derivatives.
 34. A methodaccording to claim 21, wherein the reservoir (2) stores pressurisedfluid at a pre-selected level or comprises, such as is, a pumppressurising fluid to a pre-selected level.
 35. A method according toclaim 21, wherein the method is embedded in a system according to claim1.